(1) Field of the Invention
The present invention relates to a method of activating protection means for protecting an occupant of an aircraft, and to an aircraft implementing the method.
In order to protect an occupant of an aircraft, it is possible to use protection means that are activated by activator means, e.g. a protection bag that is deployed out from a housing by deployment means, a belt co-operating with blocking means, or indeed fusible means of a structure for breaking by dedicated means. The activator means may in particular be pyrotechnic means.
It should be observed that the term “activate protection means” should be understood as an operation causing the protection means to be active. For example, deployment means activate a protection bag by inflating it, and blocking means activate a safety belt by blocking it in a position.
Safety systems are known that seek to inflate a protection bag in the event of an accident in order to protect at least one occupant of the aircraft. The protection bag is inflated by inflation means to occupy a position between the occupant of the aircraft and a wall of the aircraft so as to avoid contact between said occupant and said wall during such an accident.
An inflatable protection bag is commonly referred to as an “airbag”.
(2) Description of Related Art
Document U.S. Pat. No. 5,556,056 describes an aircraft safety system having at least one inflatable protection bag contained in a storage space. That safety system is provided with means for inflating the protection bag. The inflation means activate the protection bag as a function of the acceleration of the aircraft in order to deploy the protection bag out from the storage space.
According to document US 2001/019089, three orthogonal accelerometers are used.
Similarly, document U.S. Pat. No. 5,928,300 suggests using three accelerometers measuring the acceleration of the aircraft along three respective directions. A microprocessor deduces therefrom a longitudinal acceleration along a longitudinal direction of the aircraft, a transverse acceleration along a transverse direction of the aircraft, and an elevation acceleration along an elevation direction of the aircraft.
Furthermore, according to that document U.S. Pat. No. 5,928,300, the microprocessor initially determines whether at least one of said longitudinal, transverse, and elevation accelerations exceeds a first predetermined threshold.
When any one of said longitudinal, transverse, and elevation accelerations exceeds a first predetermined threshold, the microprocessor determines the speed variation of the aircraft in the direction of the excessive acceleration. The microprocessor requires the inflatable bags to be inflated if said variation exceeds a second predetermined threshold.
Thus, the microprocessor causes the inflatable bags to be inflated when:                the longitudinal acceleration exceeds a first longitudinal threshold and when the variation of the longitudinal speed of the aircraft along the longitudinal direction exceeds a second longitudinal threshold;        the transverse acceleration exceeds a first transverse threshold and when the variation of the transverse speed of the aircraft along the transverse direction exceeds a second transverse threshold; or        the elevation acceleration exceeds a first elevation threshold and when the variation of the elevation speed of the aircraft along the elevation direction exceeds a second elevation threshold.        
In addition, it can be understood that untimely deployment of a protection bag should be avoided.
Document WO 2004/059445A2 is also known.